Comparison of radiation sources and filtering safety glasses for fluorescent nondestructive evaluation

This study was directed toward the question of whether recent advancements in radiation sources and test media offered significant improvements over the current state of the art. Included were experiments characterizing common penetrant and magnetic particle materials to determine their fluorescent excitation spectra, and a comparison between the fluorescent excitation spectra and the emission spectra of common excitation sources. The relationship between exciter and test medium directly controls the luminance of a defect indication. As indication luminance increases, the probability of it being detected by the inspector increases. Fluorescent penetrant and magnetic particle test media were originally designed around the widely available filtered medium pressure mercury vapor lamp, which remains the standard excitation radiation source. Test media properties, and the types of available excitation sources have changed with time, and it was unclear whether present-day media was still best excited by the historical standard ultraviolet radiation source. Predictions and experimental work was performed to determine the optimal excitation source for fluorescent nondestructive testing, and to determine which safety lens option would offer the highest probability of detection. Improvement in radiation sources was primarily judged by an increase in fluorophore luminance versus background, which led to an increase in signal-to-noise ratio facilitating better indication detectability. Other factors considered were improved health and safety, and ease of use

New approaches to the measurement of chlorophyll, related pigments and productivity in the sea

In the 1984 SBIR Call for Proposals, NASA solicited new methods to measure primary production and chlorophyll in the ocean. Biospherical Instruments Inc. responded to this call with a proposal first to study a variety of approaches to this problem. A second phase of research was then funded to pursue instrumentation to measure the sunlight stimulated naturally occurring fluorescence of chlorophyll in marine phytoplankton. The monitoring of global productivity, global fisheries resources, application of above surface-to-underwater optical communications systems, submarine detection applications, correlation, and calibration of remote sensing systems are but some of the reasons for developing inexpensive sensors to measure chlorophyll and productivity. Normally, productivity measurements are manpower and cost intensive and, with the exception of a very few expensive multiship research experiments, provide no contemporaneous data. We feel that the patented, simple sensors that we have designed will provide a cost effective method for large scale, synoptic, optical measurements in the ocean. This document is the final project report for a NASA sponsored SBIR Phase 2 effort to develop new methods for the measurements of primary production in the ocean. This project has been successfully completed, a U.S. patent was issued covering the methodology and sensors, and the first production run of instrumentation developed under this contract has sold out and been delivered

Proceedings of the Second Airborne Imaging Spectrometer Data Analysis Workshop

Topics addressed include: calibration, the atmosphere, data problems and techniques, geological research, and botanical and geobotanical research

Data flow of spectral UV measurements at Sodankylä and Jokioinen

The data flow involved in a long-term continuous solar spectral UV irradiance monitoring program is investigated and structured to provide an overall view on the multiphase process from data acquisition to the final products. The program employing Brewer spectrophotometers as measuring instruments is maintained by the Finnish Meteorological Institute (FMI) ever since the 1990s at two sites in Finland: Sodankyla (67 degrees N) and Jokioinen (61 degrees N). It is built upon rigorous operation routines, processing procedures, and tools for quality control (QC) and quality analysis (QA) under continuous development and evaluation. Three distinct levels of data emerge, each after certain phase in the data flow: Level 0 denoting raw data, Level 1 meaning calibrated data processed in near-real time, and Level 2 comprising of postprocessed data corrected for all distinguishable errors and known inaccuracies. The final products disseminated to the users are demonstrated to result from a process with a multitude of separate steps, each required in the production of high-quality data on solar UV radiation at the Earth's surface.Peer reviewe

Enabling selective absorption in perovskite solar cells for refractometric sensing of gases

Perovskite solar cells are currently considered a promising technology for solar energy harvesting. Their capability to deliver an electrical signal when illuminated can sense changes in environmental parameters. We have numerically analyzed the variation of the current delivered by a perovskite cell as a function of the index of refraction of air, that is in contact with the front surface of the cell. This calculation identifies which geometrical and material structures enhance this behavior. After replacing the top transparent electrode of a solar cell by an optimized subwavelength metallic grating, we find a large variation in the responsivity of the cell with respect to the change in the index of refraction of the surrounding medium. Such a refractometric sensor can be interrogated electronically, avoiding the cumbersome set-ups of spectral or angular interrogation methods. We present an adaptation of the performance parameters of refractometric sensors (sensitivity and figure of merit) to the case of opto-electronic interrogation methods. The values of sensitivity and Figure of Merit are promising for the development of refractometric perovskite-based sensors

The impacts of optical radiation in the environment on skin: Hazards, measurement, regulation and protection

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.From 2001 to 2005, work was conducted at the Photobiology Unit at Ninewells Hospital in Dundee to examine the optical radiation environment and its implications for normal and diseased skin. Artificial sources of radiation were considered within the contexts of the hazards posed, measurement of the hazards, regulation concerning exposure and sources, and protection of abnormal skin from adversee ffects. The hazards posed by both ultraviolet (UV) and visible polychromatic sources were examined for normal and abnormal (chronic actinic dermatitis and solar urticaria) skin in an effort to predict the responses to such radiation. With current methodologiesi t was shown that responsesto polychromatic light cannot be forecast for normal and abnormal skin. Those hazards posed by light sources in the commercial sector are also considered. The sunbeds available in Perthshire and Dundee were evaluated spectroradiometrically and appropriate weighting functions applied. A case of adverse effects due to inappropriate use of an UV source is also presented and the implications are discussed. Two diode array spectroradiometers were evaluated for their potential as instruments to measure UV sources. It was shown that one instrument could be used to give measurementsw ith acceptablee rrors. However, later work with a different instrument of the same series showed that there are manufacturing issues to be resolved before these instruments are marketed for widespread use in dosimetry. Regulations governing exposure to and use of sources are considered where appropriate. Licensing of commercial sunbed parlours is suggested in order to enforce Health and Safety guidelines and the British Standard for such appliances, create a baseline for minimum standards of care within the commercial sector and safeguard public health. Lastly, it has been shown that skin sensitive to visible light can be protected with commercial makeup preparations.Funding was obtained from the Engineering and Physical Sciences Research Council, the National Physical Laboratory (NPL) and the Photobiology Unit of the University of Dundee

Characterization of diffusers and light-emitting diodes using radiometric measurements and mathematical modeling

Entrance diffusers enable good cosinusoidal angular responsivities of optical detectors. However, they also affect the position of the apparent detector receiving plane (reference plane). In this thesis, the reference planes of four spectroradiometer diffusers have been investigated and found to be located, in most cases, inside the diffuser. The reference plane shift should be taken into account in the calibration of the spectroradiometer equipped with such a diffuser. If the reference plane shifts are omitted, the measurement results may become systematically erroneous. The reference plane distance offsets correlate with their angular responsivities. Thus, with available angular responsivity data of a diffuser, the need to measure accurately the reference plane offset of the diffuser can be evaluated. The results obtained can be utilized in solar ultraviolet irradiance measurements. In the thesis, new kinds of measurement methods for characterizing photometric properties of light-emitting diodes (LEDs) have also been developed. The modified inverse-square law method has been developed for analyzing LED illuminance at varying distances. The method has been tested for several LEDs with different packages, colors and power levels. The method gives information about the LED luminous intensity, the LED directivity and the size and location of the LED virtual image source. The new method developed is useful in designing LED-based luminaires when photometric characteristics of LEDs become more reliably predicted. Pulse-width modulation (PWM) is often used to dim LEDs. An LED is driven at pulsed current and by changing the duty cycle of the current the LED brightness can be controlled. The influence of the PWM on spectral, thermal, and colorimetric properties of low-power, epoxy-encapsulated LEDs have also been investigated. In the thesis, a measurement system, with which the LED temperature at different duty cycles could be determined, was constructed. Using the experimental set-up, the peak-wavelengths and bandwidths of LEDs under the PWM control were evaluated. A blueshift of the peak wavelength and bandwidth narrowing of the LEDs were found. The changes in the emission spectra of the LEDs were concluded to be caused by the changes in the LED temperature. Apparent color shifts, which can be perceived by the human eye, were observed in emitted colors of two LEDs. The results indicate that it would be useful to include information on optical and thermal properties of pulsed LEDs more in detail in the datasheets by the LED manufacturers